In recent years, an MEMS (Micro Electro Mechanical Systems) technique has been developed which employs a micromachining technique in the field of semiconductor to form a micromachine structure in one piece with an electronic circuit. The MEMS technique is expected to be applied to filters and resonators.
Particularly, a micro mechanical resonator fabricated using such an MEMS technique is suitably used for RF wireless such as a remote key less entry system and spread spectrum communications. One exemplary MEMS filter employing a micro mechanical resonator fabricated by such a MEMS technique is disclosed in Japanese Patent Laying-Open No. 2006-41911 (Patent Document 1). The MEMS filter device described in this document includes a resonator. The resonator includes a vibrator having a square plate-like shape and disposed in parallel with a surface of a substrate and distant away from the substrate. The vibrator is supported by a cylindrical column coupled to the surface of the substrate. A fixed electrode is formed to face each side of the resonator with a predetermined interval interposed therebetween. When the fixed electrode is fed with an alternating-current voltage, electrostatic force is generated between the vibrator and the fixed electrode to vibrate the resonator. In this case, the centers and corners of the respective sides of the vibrator are transversely vibrated. In the case where the resonator is coupled to another resonator via a coupling body, the coupling body conducts longitudinal vibration.
Further, an RF-MEMS filter fabricated using a silicon process highly compatible with a semiconductor process is proposed by Hashimura Akinori et. al, “Development of Torsional-Mode RF-MEMS Filter”, IEICE Technical Report, The Institute of Electronics, Information and Communication Engineers, MW2005-185 (2006-3) (Non-Patent Document 1). This document presents that a resonator employing a torsional vibration mode is effective in achieving both a reduced size and a high Q factor.                Patent Document 1: Japanese Patent Laying-Open No. 2006-41911        Non-Patent Document 1: Hashimura Akinori et. al, “Development of Torsional-Mode RF-MEMS Filter”, IEICE Technical Report, The Institute of Electronics, Information and Communication Engineers, MW2005-185 (2006-3)        